JP6625662B2 - Phantom and method for quality assurance of particle beam therapy equipment - Google Patents

Description

  The invention relates to the field of particle beam therapy. More particularly, the invention relates to phantoms and methods for quality control of particle therapy devices used in intensity modulated particle therapy (IMPT) configurations, also known as pencil beam scanning.

In current proton beam facilities, pencil beam scanning (PBS) involves the illumination of individual spots on a target, each spot having a predetermined location and depth, and a predetermined dose prescribed for each spot. In each treatment room of the facility, various characteristics of the transmitted beam are subject to daily verification. These properties include:
Beam range: the location of the Bragg peak at a given beam energy in a given target, usually a water phantom or multilayer ionization chamber;
Spot position and spot size: measured by a suitable 2D detector, for example an array of ion chambers with a CCD camera or a scintillator screen;
-Accumulated dose: measured by an absolute ionization chamber to determine the output rate of the irradiation equipment.
Each of these properties is typically measured at a number of different beam energy levels by separate measurement devices. Complete verification requires many manual operations, including entering the treatment room to adapt the phantom or measurement device. Therefore, the time required to complete the verification work is about 30 to 60 minutes. Such a long verification time reduces the efficiency of the treatment facility with respect to the number of treatments that can be performed per day.

  The document EP 2 422 847 describes doses for the verification of irradiation beams in standard conformal irradiation (ie high energy X-rays, not particle beams) treatment, in particular IMRT (Intensity Modulated Radiation Therapy). Related to measuring devices. The device comprises an active area with a line of radiation detectors and a build-up plate with a plurality of degraders of different thickness. This device is usually designed with the specific purpose of verifying the function of a multi-leaf collimator used in a radiation therapy apparatus, but is not designed for comprehensive validation of a particle therapy apparatus. This device is not suitable for measuring the beam range of a particle beam, because the thickness of the build-up plate does not adapt to the location of the Bragg peak caused by the hadron beam of a given energy. .

  The document WO 2013160379 discloses a device and method for hadron beam verification capable of verifying the properties of the beam emitted by a particle beam therapy device, including range, spot size and spot position. I have. However, the device and method are not designed for comprehensive validation of particle therapy devices including components such as patient positioning systems, RX imaging systems, and the like. No means are provided to enable the determination of the particle beam relative to the X-ray source or the precise adjustment of the patient positioning system.

  SUMMARY OF THE INVENTION It is an object of the invention to provide a phantom and a method for quality assurance of a particle therapy apparatus used in an intensity-modulated particle therapy (IMPT) configuration to perform quick and reliable verification of the particle therapy apparatus. Is to make it possible. More precisely, there is a need for a phantom that allows the adjustment of the particle beam emitted by the particle therapy device in conjunction with two or more X-ray systems, each comprising an X-ray source and a 2D X-ray detector And

  The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

  According to a first aspect of the invention, there is provided a phantom for quality assurance of a particle beam therapy device usable in intensity modulated particle beam therapy (IMPT) mode, comprising: (a) a first surface and the first surface; A frame structure having a second surface parallel to the surface and having an edge made of RX permeable material; and (b) a first wedge surface oriented parallel to and parallel to said first surface. And one or more wedges, each having a second wedge surface oriented opposite the first surface and inclined with respect to the first surface; and (c) the first surface. A first block of material having a first block surface oriented parallel to and parallel to the first material block and a second block surface oriented parallel to and parallel to the second surface, the absolute dosimeter comprising: A first material block disposed on the first block surface; and (d) the first material block. A second block of material having a first block surface oriented parallel to and parallel to the second surface, and a second block surface oriented parallel to and parallel to the second surface; A phantom is provided, comprising: a plurality of beads of high density material located at one and / or the second block; and (f) a 2D detector located at the second face. According to the invention, the one or more wedges, the first block of material, the absolute dosimeter, the second block of material, the plurality of beads of high density material, and the 2D detector are fixed with respect to the frame structure. In position. The phantom of the invention may comprise a central bead of high density material held in a central known fixed position with respect to the frame structure, wherein the one or more wedges, the first and second blocks of material are From the first side and from above and perpendicular to it, the beam traversing the phantom through the central bead, without traversing any material other than the central bead, to the second side Is located within the frame structure to reach.

  The frame structure preferably has a polyhedral shape, and more preferably a rectangular parallelepiped.

  Visual markers may be provided at known locations on one or more of the edges.

  The one or more wedges may include a portion between the first and second surfaces having a distance provided between 20 mm and 315 mm, and may be made of a material having water equivalent radiation absorbing properties. Is preferred. By selecting such a distance, the Bragg peak of the particle beam emitted by the particle beam therapy device and penetrating through the first wedge surface will have a beam energy within the range of energies commonly used for particle beam therapy. Occurs at the second wedge surface.

  The wedge and / or the first block and / or the second block are preferably made of a material having water-equivalent radiation absorption properties. A material having water-equivalent radiation absorption properties is a material that loses the same amount of energy that a particle beam loses in water at the same penetration distance during its travel through the material.

  The 2D detector is preferably held at the edge of said second surface by a clip.

  The plurality of high density material beads are preferably metal spheres having a diameter between 1 and 3 mm.

According to a second aspect of the invention, there is provided a method for quality assurance of a particle therapy device usable in an intensity modulated particle therapy (IMPT) configuration, the device comprising: a patient positioner having a reference position; An X-ray source and two or more X-ray systems comprising a 2D X-ray detector,
a) providing a phantom according to the invention;
b) positioning the phantom on the patient positioner;
c) positioning the patient positioner at the reference position;
d) illuminating the phantom with a pencil beam directed at a known fixed position in the center of the phantom, and acquiring an image of the pencil beam on the 2D detector;
e) calculating a distance between a central bead and the pencil beam from the image.

Preferably, the method further comprises, between steps b) and c),
f) positioning the patient positioner at a known offset vector from the reference position;
g) obtaining one or more X-ray images of the phantom on the 2D X-ray detector;
h) calculating a correction vector from the image of the dense material bead on the 2D X-ray detector to move the patient positioner to the reference position;
i) verifying that the sum of the offset vectors and the correction vectors is less than a threshold.

More preferably, the method further comprises, after step c):
j) illuminating the phantom (10) with a plurality of pencil beams, each having the same energy, and acquiring an image of the pencil beam on the 2D detector (180);
k) calculating a beam range, a spot size, and a spot position from the image;
l) obtaining a radiation dose from said absolute radiation detector (130);
m) verifying that the beam range, spot size, spot position, and radiation dose are within a range from the expected beam range, spot size, spot position, and radiation dose.

Alternatively, in a method for quality assurance of a particle therapy device used in an intensity modulated particle therapy (IMPT) configuration, the device comprises a patient positioner having a reference position, an X-ray source and a 2D X-ray detector, respectively. Two or more x-ray systems comprising instruments
n) providing a phantom according to the invention;
o) positioning the phantom on the patient positioner;
p) positioning the patient positioner at a known offset vector from the reference position;
q) obtaining one or more X-ray images of the phantom on the 2D X-ray detector;
r) calculating a correction vector for moving the patient positioner to the reference position from the reference image on the 2D X-ray detector;
s) verifying that the sum of the offset vector and the correction vector is less than a threshold;
t) positioning the patient positioner at the reference position;
u) illuminating the phantom with a plurality of pencil beams, each having the same energy, and acquiring an image of the pencil beam on the 2D detector;
v) calculating a beam range, a spot size, and a spot position from the image;
w) obtaining a radiation dose from the absolute radiation detector;
x) verifying that the beam range, spot size, spot position, and radiation dose are within range from the expected beam range, spot size, spot position, and radiation dose. .

According to a preferred method, if the phantom has a visual marker at a known position on one or more edges, then the method further comprises:
a) directing one or more fans of light or laser light at the visual marker;
b) verifying the match of the fan of light or laser light with the visual recognition marker.

  Steps j) to m) may be repeated for different beam energies.

  Advantageously, at least one of steps c) to m) is performed automatically under program control.

  According to a third aspect of the invention, there is provided a computer program comprising code for performing at least some of steps c) to m) of the method of the invention.

  According to a fourth aspect of the invention there is provided a system comprising a phantom according to the invention and a controller comprising a computer program according to the invention for quality assurance of a particle therapy device.

According to a fifth and last aspect of the invention, there is provided a phantom for quality assurance of a particle beam therapy system,
a) a 2D detector for detecting particles, having an xy detector plane;
b) a wedge-shaped block having a surface parallel to the xy detector plane and a surface inclined with respect to the xy detector plane;
c) two or more imaging markers located on the first support block;
d) a second block configured to support the dosimeter detector;
The phantom further comprises a fiducial marker positioned along a line essentially perpendicular to the xy detector plane, so that the wedge-shaped block, the first block, and the second block do not obstruct the line. Located and configured.

  These and further aspects of the present invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a phantom according to an embodiment of the present invention. FIG. 2 is a perspective view of the same phantom viewed from the other side. FIG. 3 is a perspective view of the same wedge. FIG. 4 is a schematic illustration of the beam and corresponding image across the wedge. FIG. 5 is a schematic illustration of a central bead and corresponding image of the same phantom. FIG. 6a is a schematic illustration of a phantom at a known offset position. FIG. 6b is a schematic diagram of the phantom in the reference position. FIG. 7a is a schematic diagram of a plurality of irradiated pencil beams. FIG. 7b is the corresponding image. FIG. 8 is a detailed view of the means for fixing the film to the frame structure.

  The depictions in the figures are not drawn to scale or to scale. Generally, identical components are denoted by the same reference numerals in the figures.

  FIG. 1 is a perspective view of a phantom 10 according to an embodiment of the present invention. The frame structure 30 comprises a series of edges 40, which in the embodiment shown forms a rectangular parallelepiped polyhedron. The first face of the cuboid may use a beam incidence face, ie, this face is oriented towards the beam source when a phantom is used. These edges are made of, for example, an X-ray transmitting material such as carbon fiber, and are assembled without using metal pieces, for example, by bonding. The phantom 10 includes a series of wedges 70 described later. The phantom includes a first block of material 100 having a first surface 110 and a second surface 120 that are parallel to the first 50 and second 60 surfaces of the frame structure 30, respectively. An absolute dosimeter 130 is located and may be used to measure the dose emitted by the first face 110 of this first block and the beam source. An ionization chamber may be used as an absolute dosimeter. Between the first block of material 110 and the second block of material 140, the beam passes through the first face 50 and enters the phantom 10 perpendicular to them, and the first 50 of the frame structure 30. And without crossing any material, except for a central high density material bead located along the centerline of this channel, conveniently located on a line passing through the center of the second 60) plane. Open channels are provided to allow passage. This central bead 175 is conveniently placed in this position through one of the components of the phantom 10, for example, through a rod of x-ray transparent material mounted on a second block 140, as shown in FIG. May be retained. In addition to the center bead 175, a set of additional beads 170 are located at known locations within the phantom. In the embodiment shown, two beads 170 are located on the first surface 150 of the second block 140 and two beads 170 are located on the top surface of the first block 100. The function and role of these beads 170, 175 will be described with respect to the method of the invention. By "dense material" is meant a material having a density greater than 1 such that the bead is visible by x-ray imaging and with a 2D detector under the particle beam. Beads made of metal, for example steel, are convenient for this purpose. The use of spheres in the 1-3 mm range, for example 2 mm, has been found to be advantageous to provide sufficient visibility in the image and good accuracy in positioning. The beads may be fixed in holes drilled in the block of material. A viewing marker 200 may be provided at a known location on the edge 40 of the frame structure 30. The function and use of these visual markers 200 will be discussed below.

  FIG. 2 is a perspective view of the same phantom, showing the same components and viewed from the other side. In the embodiment shown, four wedges are provided, the second wedge surface 90 being inclined at a 24 ° angle to the second surface 60 of the frame structure 30. A second face 120 of the first block 100 and a second face 160 of the second block have appeared.

  FIG. 3 is a perspective view of a wedge of the phantom of FIG. The two upper wedges have a beam path length of 65 mm at the top and 20 mm at the bottom, and a path length of 42.5 mm at an intermediate height. If the wedge is made of a water equivalent material, this corresponds to the depth of the Bragg peak of the proton beam with an energy of 73.37 MeV. Similarly, the bottom right wedge is dimensioned to have a path length of 82.5 mm at an intermediate height corresponding to an energy of 106.4 MeV, while the bottom left wedge has a Bragg peak at an energy of 172.53 MeV. It is dimensioned to have a path length of 192.5 mm at the corresponding intermediate height. For example, additional blocks having lengths of 70 mm, 100 mm, 200 mm, and 250 mm have 142.25 mm, 242 at intermediate heights, corresponding to Bragg peak depths of 145.13 MeV, 197.22 MeV, 220.9 MeV, respectively. .50 and 292.50 mm may be added to the upper wedge (via the dovetail assembly shown). As is known in the art, particle therapy devices are designed to treat tumors located at a range of depths within a patient. Therefore, the device is designed to be able to generate a particle beam having an energy range that produces a Bragg peak depth corresponding to the depth of said range. Those skilled in the art will know how to select one or more wedge dimensions to measure the range of beam energies required to verify a particle therapy device.

  FIG. 4 illustrates a method for determining beam energy using the phantom and method of the invention. The beam (or series of individual pencil beams) is directed at the first face 80 of the wedge or wedges. The dose accumulated on the 2D detector after the beam passes through the wedge is measured. The height at which the detected dose is at a maximum corresponds to the Bragg peak, and the corresponding path length 210 at the wedge provides the Bragg peak depth corresponding to the beam energy in a known manner.

  Use the phantom of the invention to effectively and quickly verify the function of components of a radiotherapy device, including X-ray imaging sources and detectors, positioning systems, and control systems used to manage these components. It is possible to do. The phantom is positioned at a nominal position on the patient positioner (patient table). The patient positioner is positioned at a known offset from the reference position. This offset position may include spatial translation (x, y, z) as well as angular orientation and orientation. The x-ray imaging system is then used to take a picture of the phantom, and from the images of the beads 170, 175 on the x-ray detector, the correction vector may be calculated in a known manner. Offset additions and corrections (translation and rotation) should be zero, and any deviation from zero should be treated as a potential initial value in the system. All these steps may be advantageously performed under program control. The acquired X-ray images may be processed by a program to calculate a correction vector. The patient positioner is then moved to the reference position. This reference position may be such a position that the 2D detector is positioned at the isocenter of the particle beam therapy system. At this stage, and an additional check may be made to verify that the phantom is in the correct position: a set of (laser) light sources are installed around the reference position at a fixed and known position. Direct the fan beam of (laser) light. The light source is installed and directed to reach a viewing marker 200 on the edge of the frame structure 30. The images of these fan beams on these markers 200 are checked to make sure that the phantom is in the correct position. Again, these steps, including image acquisition and processing, may be advantageously performed automatically and under program control. 6a and 6b are schematic illustrations of a phantom at a known offset position and a reference position, respectively.

  The function of the center bead 175 will now be discussed. When the phantom is positioned at the reference position, the particle beam is directed along the center line in the phantom. The corresponding image obtained from the 2D detector is shown in the center of FIG. 5, and the corresponding histogram is shown in the right part of FIG. The peak corresponds to the beam, and the centroid of this peak can be determined, for example, by taking the midpoint between two points located at the mid-height of the peak. The valley at the top of the peak results from the absorption caused by the bead 175. The center of this valley corresponds to the bead position. This histogram allows verification of the beam adjustment to the geometry adjustment performed by the X-ray system. The centroid of the beam peak must coincide with the center of the valley at the peak apex caused by the central bead 175. The steps of controlling the direction of the central beam, acquiring the 2D detector, and processing the image to provide a verification signal may be performed automatically under program control.

  FIG. 7a shows a series of beams generated under program control by a radiation therapy device and directed at a phantom in a reference position. FIG. 7b shows the corresponding image obtained from the 2D detector. From these images, different parameters, such as beam energy and adjustment, as discussed above, may be obtained. Further, the spot size and the position may be verified by a known method.

  The presence of the frame structure 30 in the inventive phantom 10 has many advantages: the phantom is easily maneuverable, and the frame is reliable with respect to the location of the various components of the phantom. The marker 200 enables accurate position verification by laser light. In addition, the rim 40 may be used to attach components to the frame: the 2D detector is a film detector that is held to the frame via a plastic clip 220, as shown in FIG. There may be. The 2D detector may also be a scintillator-based detector with a camera and may be attached to the frame via a clip 220.

  By using the phantom and the method of the invention, the components of the device, such as the positioning system, the X-ray imaging system, the beam directing system, the function of the particle beam therapy device including the dose, and the daily verification of the dose can be reliably determined. It is possible to do. When performed under program control, the method is particularly effective and fast, with a complete quality assurance in less than 10 minutes. The method of the present invention eliminates the need for the treating physician to enter the treatment room to make changes to the phantom and to exit the treatment room to make measurements, and the like.

  Although the invention has been described with reference to particular embodiments, it is illustrative of the invention and should not be construed as limiting. More generally, it will be appreciated by those skilled in the art that the present invention is not limited by what has been particularly shown and / or described above.

  The reference signs in the claims do not limit their scope of protection. Use of the verbs "comprise," "includes," "consists of," or any other modification thereof, as well as their respective inflections, does not exclude the presence of other elements described. Use of the article "a", "an", or "the" before an element does not exclude the presence of a plurality of such elements.

Claims (20)

A phantom (10) for quality assurance of a particle beam therapy device usable in an intensity modulated particle beam therapy (IMPT) mode,
a) a frame structure (30) having a first surface (50) and a second surface (60) parallel to said first surface and having an edge (40) made of RX permeable material; ,
b) a first wedge surface (80) oriented with and parallel to said first surface, and oriented opposite to said first surface and inclined with respect to said first surface (50). One or more wedges (70) each having a second wedge (90) surface to be provided;
c) a first block surface (110) oriented parallel to and parallel to the first surface, and a second block surface (120) oriented parallel to and parallel to the second surface (60). A first material block (100) having an absolute dosimeter (130) disposed on said first block surface (110);
d) a first block surface (150) oriented with and parallel to said first surface and a second block surface (160) oriented with and parallel to said second surface (60). A second material block (140) comprising:
e) said first (1 0 0) and / or a plurality of beads of high density material positioned in said second block (140) and (170),
f) a 2D detector (180) disposed on the second surface;
The one or more wedges (70), a first block of material, an absolute dosimeter, a second block of material, a plurality of beads of high density material (170), and a 2D detector (180) are provided on the frame structure. In a phantom (10) in a known fixed position with respect to (30),
A central bead of high density material (175) is held in a central, known fixed position with respect to the frame structure (30), and the one or more wedges (70), the first (100) and the second material The block (140) includes a beam that traverses the phantom (10) through the central bead (175) and from the first surface (50) and perpendicular to the other of the central bead (175). Disposed within the frame structure (30) so as to reach the second surface (60) without traversing any of the materials.
A phantom characterized by that.   The phantom (10) according to claim 1, wherein the frame structure (30) is polyhedral.   3. The phantom according to claim 2, wherein the polyhedron is a cuboid.   A phantom (10) according to any one of the preceding claims, wherein a visual marker (200) is provided at a known location on one or more of said edges (40).   The phantom (10) according to any of the preceding claims, wherein the one or more wedges (70) are connected to the first wedge surface (80) and the second wedge surface (90). A phantom comprising a portion (210) between them having a distance provided between 20mm and 315mm and made of a material having water equivalent radiation absorption properties.   The phantom (10) according to any one of the preceding claims, wherein the one or more wedges (70) and / or the first block (100) and / or the second block (140). Is a phantom made of a material having water equivalent radiation absorption characteristics.   The phantom (10) according to any of the preceding claims, wherein the 2D detector (180) is held on the edge (40) of the second surface (60) by a clip (220). A phantom characterized by being performed.   Phantom (10) according to any of the preceding claims, wherein the plurality of high density material beads (170, 175) are metal spheres having a diameter between 1 and 3 mm. And a phantom. A method for quality assurance of a particle therapy device usable in an intensity modulated particle therapy (IMPT) configuration, the device comprising a patient positioner having a reference position, and an X-ray source and a 2D X-ray detector, respectively. And two or more x-ray systems comprising:
a) providing a phantom (10) according to any one of claims 1 to 8;
b) positioning the phantom (10) on the patient positioner;
c) positioning the patient positioner at the reference position;
d) illuminating the phantom (10) with a pencil beam directed at a known fixed position in the center of the phantom and acquiring an image of the pencil beam on the 2D detector (180);
e) calculating a distance between the central bead (175) and the pencil beam from the image;
A method comprising: 10. The method according to claim 9, further comprising, between steps b) and c):
f) positioning the patient positioner at a known offset vector from the reference position;
g) obtaining one or more X-ray images of the phantom (10) on the 2D X-ray detector;
h) calculating a correction vector for moving the patient positioner to the reference position from the image of the dense material bead (170, 175) on the 2D X-ray detector;
a step of verifying that i) of the offset vector, and, the sum of the correction vector is less than the threshold value,
A method comprising: 11. The method according to any one of claims 9 or 10, further comprising after step c):
j) illuminating the phantom (10) with a plurality of pencil beams, each having the same energy, and acquiring the image of the pencil beam on the 2D detector (180);
k) calculating a beam range, a spot size, and a spot position from the image;
l) obtaining a radiation dose from said absolute radiation detector (130);
m) verifying that the beam range, spot size, spot position, and radiation dose are within a range from the expected beam range, spot size, spot position, and radiation dose;
A method comprising: The method according to any one of claims 9 to 11, wherein the phantom (10) comprises a visual marker (200) at a known location on one or more of the edges (40), the method further comprising: ,
n) directing one or more fans of light or laser light toward the viewing marker (200);
o) verifying the match of the fan of light or laser light with the visual marker (200);
A method comprising: The method of claim 11 , further comprising repeating steps j) to m) for different beam energies. 10. The method according to claim 9 , wherein at least one of steps c) to e) is performed automatically under program control. 11. The method according to claim 10, wherein at least one of steps f) to i) is performed automatically under program control. The method according to claim 11, wherein at least one of steps j) to m) is performed automatically under program control. 13. The method according to claim 12, wherein at least one of steps n) to o) is performed automatically under program control. 14. The method according to claim 13, wherein at least one of steps j) to m) is performed automatically under program control. Steps c) to e) according to claim 9 and / or steps f) to i) according to claim 10 and / or steps j) to m) according to claim 11 and / or claim 12. Computer program comprising code for performing steps n) to o) of the above. A system comprising a phantom (10) according to any one of claims 1 to 9 and a controller comprising a computer program according to claim 19 for said quality assurance of a particle therapy device.

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